The Montreal Protocol for the protection of the ozone layer mandated the phase-out of the use of chlorofluorocarbons (CFCs). Materials more “friendly” to the ozone layer, such as hydrofluorocarbons (HFCs), e.g., HFC-134a, replaced chlorofluorocarbons. The latter compounds have proven to be green house gases, causing global warming, and were regulated by the Kyoto Protocol on Climate Change. The emerging replacement materials, hydrofluoropropenes, were shown to be environmentally acceptable, i.e., they have zero ozone depletion potential (ODP) and acceptable low global warming potential (GWP).
Currently used blowing agents for thermoset foams include HFC-134a, HFC-245fa, HFC-365mfc, which have relatively high global warming potential, and hydrocarbons such as pentane isomers, which are flammable and have low energy efficiency. Therefore, new alternative blowing agents are being sought. Halogenated hydroolefinic materials such as hydrofluoropropenes and/or hydrochlorofluoropropenes have generated interest as replacements for HFCs. The inherent chemical instability of these materials in the lower atmosphere provides for a low global warming potential and zero or near zero ozone depletion properties desired.
It is convenient in many applications to provide the components for polyurethane or polyisocyanurate foams in pre-blended formulations. Most typically, the foam formulation is pre-blended into two components. The polyisocyanate and optional isocyanate compatible raw materials comprise the first component, commonly referred to as the A-side component. A polyol or mixture of polyols, surfactant, catalyst, blowing agent, and other isocyanate reactive and non-reactive components comprise the second component, commonly referred to as the B-side component. Accordingly, polyurethane or polyisocyanurate foams are readily prepared by bringing together the A- and B-side components either by hand mix for small preparations and, preferably, machine mix techniques to form blocks, slabs, laminates, pour-in-place panels and other items, spray applied foams, froths, and the like.
Two-component systems, however, have been found to have reduced shelf-life of the B-side composition, especially those systems which use certain hydrohaloolefins, such as, for example, HFO-1234ze and HCFO-1233zd. Normally when a foam is produced by bringing together the A- and B-side components, a good foam is obtained. However, if the polyol pre-mix composition is aged prior to treatment with the polyisocyanate, the foams are of lower quality and may even collapse during the formation of the foam. The poor foam structure is attributed to the reaction of certain catalysts with certain hydrohaloolefins, including HFO-1234ze and HCFO-1233zd, which results in the partial decomposition of the blowing agent and, subsequently, the undesirable modification of the polymeric silicone surfactants.
One way to overcome this problem, for example, is by separating the blowing agent, surfactant, and catalyst, and introducing them using a separate stream from the A- or B-side components. However, a preferred solution would not require such reformulation or process change. A more favorable method may be to stabilize the polyol pre-mix composition to help prevent the decomposition of the blowing agent. As certain catalysts are now known to have a detrimental effect on the halogenated olefinic blowing agents, a stable polyol pre-mix composition is desired which will reduce or eliminate such detrimental interactions. Additionally, a method for stabilizing thermosetting foam blends, the resulting stable pre-mix blend formulations, and the environmentally-friendly polyurethane or polyisocyanurate foams having good foam structure remain highly desirable.